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Tis’ the HVAC Season

Tis’ the HVAC Season

By: DrPeter

Intro:
In this Tech Tip I will be explaining some quick and easy diagnostic tips for the Volkswagen/Audi HVAC systems. We will be focusing on the systems that are diagnosable with the VCDS scan-tool. Even though the system designs maybe slightly different between brands and models, they are generally similar enough that we can diagnose them using the information contain herein. It is always advisable to use the current repair information and training materials available and understand the system that you are working on, a little time spent learning will save you a lot of wasted time fixing your mistakes when you could have been fixing the vehicle.

Warning:
Yep, got to say this stuff because frostbite hurts more when the flesh thaws and blindness caused by refrigerant gases blasting out at 400psi can really suck when trying to work on cars, so... As with any potentially hazardous system of the automobile, we must remember to follow all of the manufacture’s safety, caution and warning notices found in the Factory Repair information. Also pay attention to any local, state or government laws regarding properly trained and/or licensed personal when working with regulated materials, such as refrigerants. If you do NOT know what you are doing or have not been properly trained, STOP! HALT! ARRÊT ¡ALTO! 停止

Training:
I have been trained in many aspects of the automotive and commercial HVAC systems (and living in SW Florida helps, AC season 365). I suggest anyone who is working with the HVAC systems in the Automotive world to get the right training and certifications, in 1993 I became a member of http://www.macsw.org , Mobile Air Conditioning Society (MACS) Worldwide, went to the class and became certified, so I suggest to cover your butt!

Diagnose first, then fix:
Diagnosing the modern Volkswagen/Audi HAVC system can be a bit challenging at times, certainly not impossible and troubleshooting is now easier with newer HVAC Controllers having more diagnostic capabilities compared to older generations. Yes, I will try to do a small tech tip on the older MK4 systems, though these systems are not completely diagnosable with the VCDS tool.
Here are the quick and easy checks you can use to help identify the cause of the concern within the HVAC system.

1) Check the basics in the [08-Auto HVAC] controller with VCDS.

Address any fault codes accordingly, use the Ross-Tech wiki and or repair manual

The best way to check AC system pressure is to use a good quality AC Gauge set. Verify the system has pressure, because the Refrigerant Pressure Sensor G65 maybe incorrect and the MVB data could show a different pressure. Also remember what Jef says, check the charge, pressure will not indicate a full charge.

Learn how to read the gauges, it is like reading between the lines, it will tell you a lot!

4) Check for proper operation of cooling fans

In many vehicles an [01-Engine] [Output Test] will activate BOTH fans, if equipped

The HVAC system in many cases will not function when the fans have failed. Check ECM for codes too.

5) Check for damage:

Compressor shaft is spinning (shear hub is not damaged)

Wiring, connections’

Hoses, fittings and missing valve caps(primary seal)

Addition notes, tips:

On some 2006 to 2009 vehicles it may be necessary to reset the Temperature Sensor, this can occur when the AC controller or ambient temperature sensor were replaced. To reset the Temperature Sensor, drive the vehicle above 30mph or let the vehicle sit, engine idling, for about 20 minutes.

2012 and newer Jetta sedans may have a customer concern of A/C shutting off when coming to a stop. When checking the HVAC controller for the Compressor Shut off code, [12- Shut-Off requested by Engine Control] maybe found, this is usually considered normal, the ECM is programmed to command the HVAC controller to shut off the compressor to allow increased engine rpm/vacuum when braking, mostly when the engine is cold, pre-catalyst operating temperature.

If your compressor shut off code is [0], check the N280-Refrigerant Regulating Valve** valve, this is what regulates the amount of refrigerant that the compressor ‘pumps’ through the system. The N280-Refrigerant Regulating Valve activation signal can be checked with an incandescent light bulb in its place. Unplug the N280-Refrigerant Regulating Valve, connect a test bulb to the connector from the HVAC controller and start the vehicle, turn on the AC and watch for the activation command from the HVAC controller. If the bulb lights and the compressor had failed to operate prior, then the N280-Refrigerant Regulating Valve and/or compressor has most likely failed.

The newer HVAC systems use a pressure sensor – G65, not a pressure switch. The G65 can send information about the refrigerant pressure to the HVAC controller, a pressure switch, like the F129 cannot.

Located in the same place as the F129, the G65 is different, yet does the same functions as the F129.

It uses a pressure sensor and a microprocessor to create a PWM (Pulsed-width Modulated) signal

Pin 1 & 3 provide Ground and Power, PWM signal is on Pin2.

Update: August 31, 2015

The following Information has been deemed useful:- 2006+ Volkswagen New Beetle/Convertible, the N280-Refrigerant Regulating Valve is controlled by the ECM.
Use Measuring Value Block 135, 136 and 137 for information about,
... the Duty cycle of the coolant fan
... the Relay 1 for the coolant fan
... the coolant fan after-run
... Condition of the AC
... Condition of the AC Compressor
... A/C-Pressure
... Fan request from A/C-System

-2006 to 2010 Volkswagen New Beetle/Convertible.
Fault codes P2612 and P2613 - may caused by wiring connections and or wiring harness routing/damage.
see the Ross-Tech wiki page for more information.

2009 A5 3.2 6 speed in AC hell. AC was working fine. Car sat idle for a few weeks, started car, no AC. Car has just over 75K miles, I have worked on my own AC for some time now as it seems every car I own has AC problems. I am not by any means an expert but I do okay, used to a 1967 Chrysler where if the compressor was bad you could pull the head on it and replace the reed valves. I am, however, a high mileage driver (put 290K on my 98 2.8 A4 stick, mostly NYC miles- two Denso compressors). Seems the A5 does not have an AC clutch, but rather a drive hub. I cannot see a wire going to it and cannot find one on the electrical diagram or a fuse for it (Bentleys). I could not get a signal going to the N280 Regulator valve with a Fluke VOM (Did read a small signal 0.07V DC, reading measuring blocks it was switching 0-.7 Amp reading 8.6 Bar). Bentleys calls for using an oscilloscope looking at the square wave, apparently runs off pulse width (PWM). Going through measuring blocks did not see much for labels of what I was looking at. I do take suggestions.
At stand still I am measuring about 85 PSIG high and low side with gauges which would appear to be a full charge, 80 deg. F.
I am posting the autoscan Previous fault codes were the right door lock, Headlight leveler, radio codes, (works fine), seat memory (who cares) and the left floorwell flap motor as below.
I hope I pasted this okay.
I sincerely appreciate any and all help. I am also going by Audi in the morning and will attempt to talk to a tech.
Rich

I am posting the autoscan Previous fault codes were the right door lock, Headlight leveler, radio codes, (works fine), seat memory (who cares) and the left floorwell flap motor as below.

Your symptoms and your DTCs align closely with a known issue on that G395 sensor. Apparently it's common for the wiring to that sensor to fail or be damaged. Audi put out a TSB which you can find on AudiWorld thread attached to post #6.

You do have a stack of other interesting faults, and the above doesn't explain the G238 sensor error. Has the car been in a collision, or had water damage? The TSB indicates a probable wiring problem, but your damage location might not be one of the common ones.

Thanks, I'm trying to retrieve the TSB unsuccesfully, I am not a member of AudiWorld, I am not sure why I cannot access it from my ebahn bentleys manual.I emailed them. Audi took my VIN number and told me this morning there were no TSB's on the AC for the car.
Thanks again for your help.
Rich

Thanks I'm printing it out now. I was also going to call Ross Tech and pay for support to help me with analyzing the signals (if any), perhaps that's why I'm not getting the proper measuring block information.
Rich

Thanks I'm printing it out now. I was also going to call Ross Tech and pay for support to help me with analyzing the signals (if any), perhaps that's why I'm not getting the proper measuring block information.
Rich

The "Labels: Redir Fail!" text in the address 08 scan means it found a pointer to where the label file should be, but could not find the label file itself. In your case, it's looking for the file 8Tx-820-043-3Z.CLB. I did a bit of Googling and it looks like VCDS has files similar to that in at least two regional translated versions of VCDS, but not in English. That leaves one of two possibilities: there was a packaging oops and the English label file didn't make it into the installer, or the initial label file work was done in a foreign language and hasn't been translated into English yet.

Either way, I suspect this is something Ross-Tech can help you with very easily.

The linked attachment in Bernard's AC not working on 2008 VW Jetta TDI thread should be helpful for Mk5 (1K chassis) VW diagnosis including similar vehicles such as the (8P) A3 and (8J) TT which used Golf based CAN protocol #08 modules.